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/*
** blendxor.c - Demonstrates the use of the blend_logic_op
** extension to draw hilights. Using XOR to draw the same
** image twice restores the background to its original value.
*/
#include <stdio.h>
#include <string.h>
#ifndef _WIN32
#include <unistd.h>
#endif
#include <stdlib.h>
#include <GL/glut.h>
GLenum doubleBuffer;
int dithering = 0;
GLint windW, windH;
static void Init(void)
{
glDisable(GL_DITHER);
glShadeModel(GL_FLAT);
}
static void Reshape(int width, int height)
{
windW = (GLint)width;
windH = (GLint)height;
glViewport(0, 0, (GLint)width, (GLint)height);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluOrtho2D(0, 400, 0, 400);
glMatrixMode(GL_MODELVIEW);
}
static void Key(unsigned char key, int x, int y)
{
switch (key) {
case 27:
exit(1);
case 'd':
dithering = !dithering;
break;
default:
return;
}
glutPostRedisplay();
}
static void Draw(void)
{
int i;
glDisable(GL_BLEND);
(dithering) ? glEnable(GL_DITHER) : glDisable(GL_DITHER);
glClearColor(0.5, 0.6, 0.1, 1.0);
glClear(GL_COLOR_BUFFER_BIT);
/* Draw background prims */
glColor3f(0.1, 0.1, 1.0);
glBegin(GL_TRIANGLES);
glVertex2i(5, 5);
glVertex2i(130, 50);
glVertex2i(100, 300);
glEnd();
glColor3f(0.5, 0.2, 0.9);
glBegin(GL_TRIANGLES);
glVertex2i(200, 100);
glVertex2i(330, 50);
glVertex2i(340, 400);
glEnd();
glEnable(GL_BLEND);
glBlendEquationEXT(GL_LOGIC_OP);
glLogicOp(GL_XOR);
/* Draw a set of rectangles across the window */
glColor3f(0.9, 0.2, 0.8);
for(i = 0; i < 400; i+=60) {
glBegin(GL_POLYGON);
glVertex2i(i, 100);
glVertex2i(i+50, 100);
glVertex2i(i+50, 200);
glVertex2i(i, 200);
glEnd();
}
glFlush(); /* Added by Brian Paul */
#ifndef _WIN32
sleep(2);
#endif
/* Redraw the rectangles, which should erase them */
for(i = 0; i < 400; i+=60) {
glBegin(GL_POLYGON);
glVertex2i(i, 100);
glVertex2i(i+50, 100);
glVertex2i(i+50, 200);
glVertex2i(i, 200);
glEnd();
}
glFlush();
if (doubleBuffer) {
glutSwapBuffers();
}
}
static GLenum Args(int argc, char **argv)
{
GLint i;
doubleBuffer = GL_FALSE;
for (i = 1; i < argc; i++) {
if (strcmp(argv[i], "-sb") == 0) {
doubleBuffer = GL_FALSE;
} else if (strcmp(argv[i], "-db") == 0) {
doubleBuffer = GL_TRUE;
} else {
printf("%s (Bad option).\n", argv[i]);
return GL_FALSE;
}
}
return GL_TRUE;
}
int main(int argc, char **argv)
{
GLenum type;
char *s;
char *extName = "GL_EXT_blend_logic_op";
glutInit(&argc, argv);
if (Args(argc, argv) == GL_FALSE) {
exit(1);
}
glutInitWindowPosition(0, 0); glutInitWindowSize( 400, 400);
type = GLUT_RGB;
type |= (doubleBuffer) ? GLUT_DOUBLE : GLUT_SINGLE;
glutInitDisplayMode(type);
if (glutCreateWindow("Blend XOR") == GL_FALSE) {
exit(1);
}
/* Make sure blend_logic_op extension is there. */
s = (char *) glGetString(GL_EXTENSIONS);
if (!s)
exit(1);
if (strstr(s,extName) == 0) {
printf("Blend_logic_op extension is not present.\n");
exit(1);
}
Init();
glutReshapeFunc(Reshape);
glutKeyboardFunc(Key);
glutDisplayFunc(Draw);
glutMainLoop();
return 0;
}
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